1. Field of the Invention
The present invention relates to a fuel supply control apparatus for an internal combustion engine which controls a fuel supply section for directly injecting fuel to a combustion chamber of each cylinder of the internal combustion engine. More particularly, it relates to a fuel supply control apparatus for an internal combustion engine in which highly accurate fuel pressure control can be achieved by controlling an effective stroke related to a discharge stroke of a fuel supply section with high accuracy.
2. Description of the Related Art
In general, a positive displacement fuel supply device in the form of a high pressure pump is used in a fuel supply control apparatus for an internal combustion engine for directly injecting fuel from an injector installed in a combustion chamber of each cylinder into the corresponding combustion chamber.
In such a known fuel supply control apparatus for an internal combustion engine, the high pressure pump is driven to operate by a pump cam that is driven to rotate by means of the internal combustion engine in synchronization with the rotation of a camshaft, the amount of fuel discharged by the pump is changed by changing ON and OFF periods of an electromagnetic valve during the discharge stroke of the pump.
At this time, the ON and OFF periods of the electromagnetic valve are changed by using a crank angle signal from a crank angle sensor.
In addition, the pump discharge stroke can be changed in synchronization with a valve timing control device, and such a change in the pump discharge stroke in this case is carried out by changing the ON/OFF timing of the electromagnetic valve according to an estimated value from detected valve timing (for instance, see a first patent document: Japanese patent laid-open No. 2000-161115).
Further, the positive displacement fuel supply section is controlled by an effective stroke changing section so as to adjust an effective stroke (i.e., an amount of discharge) of the pump related to the discharge stroke thereof, and the effective stroke changing section is constructed of an opening and closing timing decision section of a spill valve.
Hereinafter, reference will be made to a method of deciding the opening and closing timing of the spill valve that adjusts the amount of fuel discharged from the fuel supply section in the form of a high pressure pump.
First of all, an estimated value dlvvt of the amount of change of the valve timing is calculated by the following expression (1).dlvvt=(VT−VT[i−1])+(VTT−VT)  (1)where VT represents valve timing, VT[i−1] the last valve timing, and VTT target valve timing.
Subsequently, a reference valve-opening time afpons of the spill valve is calculated by the following expression (2).afpons=afpoffs+awonbs−aoffset  (2)where afpoffs represents a reference valve-closing time of the spill valve, and awonbs represents a valve-closing period of the spill valve, these pieces of information being stored as respective MAP data in a ROM. In addition, aoffset represents an amount of offset or distance from a reference position of the camshaft to a nose of the pump driving cam.
Then, a temporary valve-closing time afponb of the spill valve is calculated by the following expression (3) in consideration of an amount of operation of the valve timing.afponb=afpons+VT  (3)
Subsequently, an amount of correction kaon for correcting the temporary valve-closing time afponb of the spill valve is calculated by the following expression (4).kaon=(dlvvt/360)×(QT+kacal−afponb)  (4)where QT represents valve-opening and valve-closing time calculation timing, and kacal represents a crank angle from the time of detection of VT to the valve-opening and valve-closing time calculation timing QT.
Thereafter, an amount of correction kaonw in the valve-opening period of the spill valve is calculated by the following expression (5).kaonw=(dlvvt/360)×awonb  (5)where awonb represents a valve-opening period of the spill valve.
Subsequently, a valve-closing timing afpon of the spill valve is calculated by the following expression (6).afpon=afponb+kaon  (6)
Finally, a final valve closing period awon of the spill valve is calculated by the following expression (7).awon=awonb+kaonw  (7)
The final valve closing period awon of the spill valve calculated from expression (7) above becomes an effective discharge period of the high pressure pump.
The known fuel supply control apparatus for an internal combustion engine as described above is constructed such that the reference valve opening and closing times afpons, afpoffs of the spill valve are calculated based on the crank angle signal, and corrected in accordance with the amount of operation of the valve timing control device. Therefore, there is a problem that the control and calculation of the opening and closing timings of the spill valve became complicated.
Moreover, since the calculation timing of the opening and closing times of the spill valve is in synchronization with the crank angle signal, there is another problem that it is necessary to control both the opening timing and closing timings of the spill valve with respect to a change in the valve timing, thus resulting in a further complication of control and calculations.
Furthermore, in order to control both of the opening and closing timings of the spill valve, it is necessary to decide the opening and closing timings at extremely earlier timing than the time required for actual control, and hence there is a further problem that the error between the estimated value and the actual value becomes large, thus deteriorating fuel pressure controllability of the fuel to be supplied in the injectors.